Accumulative Effects of Manure and N on Continuous Corn and Clay Soil. I. Growth, Yield, and Nutrient Uptake of Corn

Four rates of manure and five rates of N were applied yearly in a factorial arrangement to a Panton clay soil (Typic Ochraqualf). Applications of 120 kg/ha of P and 90 kg/ha of K were made each year to all plots. The plots were planted to corn (Zea mays L.). The objectives of the study were to study the effects of continuous corn and manure and N treatments on the physical and chemical properties of the soil and on the growth, yield, and mineral composition of the corn plants over a period of at least 5 years. The results for the latter objective are reported in this paper. During years of normal or less than normal rainfall (1965–67), manure application significantly increased yields of corn grain and stover. Averaged over all treatments of N, plots receiving 66 tons/ha of manure yielded 2.04 tons/ha more than no-manure plots. This response is especially significant in that basic applications of P and K had been made and starter P used at planting each year. For these years, the first increment of N (56 kg/ha) increased yields on unmanured plots. Higher applications of N reduced yields. Where manure was applied, there was no significant response to N. During relatively wet years (1968–69), manure had beneficial effect on corn growth and yield. The highest, or 66 ton/ha, manure application appeared to be detrimental, particularly where N had been applied. Nitrogen, on the other hand, significantly increased growth rate and yield of corn grain and stover at all levels of manure. For example, plots receiving 224 kg/ha of N yielded 5.51 tons/ha more than no-N plots. Manure treatments increased percentage K by as much as 0.30% in the corn ear leaves but decreased Ca and Mg. Manure had little effect on percentage N and P. In 1969, a wet year, manure reduced N from 2.72 to 2.44% when averaged over all treatments of N. Chemical analysis of small plants showed the same trends as did analysis of ear leaves. Percentages of Al and Fe were high. But Al varied proportionally to applied N and inversely to manure. For all treatments of N, manure decreased Al from 139 to 85 ppm. Manured plots were slightly but consistently higher in soil moisture. Small differences of about 1% were measured when the soil was near saturation (43% moisture). Differences of 2.5% were measured 1 week later when the soil was near 30% moisture.